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The base of the natural logarithm function.  Equals 2.718281828.....
can be found from the series 2 + 1/2! + 1/3! + 1/4! + 1/5! + ...........


A number that indicates the shape of a conic section. The eccentricity of  an ellipse is given by e  =  sqrt(a2 - b2) a

Eccrine glands

Sweat glands linked to the Sympathetic nervous system and widely distributed over the body surface.

EC 50

The molar concentration of an agonist, which produces 50% of the maximum possible response for that agonist.


A technique using ultra high frequency sound waves (beyond human hearing), similar to "sonar", to form an image of the inside of the heart.
This procedure can demonstrate valve damage, congenital (before birth) defects and other abnormalities.


A meaningless repetition or imitation of words that are heard. Typical echolalia tends to be repetitive and persistent. The echo is often uttered with a mocking mumbling or staccato intonation. Echolalia should not be confused with habituation repetition of questions, apparently to clarify the question and formulate its answer, as when a patient is asked, "When did you come to the hospital?" and replies "Come to the hospital? Yesterday." Echolalia is observed in some pervasive developmental disorders, organic mental disorders and in schizophrenia.


A specific characteristic biological system in a location or area with a unique mix of living organisms and physical consistency such as minerals, soil and air.


A locally adapted variant of a species, differing genetically from other ecotypes of the same species.


The outer layer of cells in embryonic development, derived from the inner cell mass (see blastocyst). It gives rise to the skin, brain, nervous system, inner ear, and lens of the eye.


An animal such as a reptile, fish, or amphibian, that must use environmental energy and behavioral adaptations to regulate its body temperature.


parasitoid that lays its eggs on the surface of the host. Larvae feed on the host from the outside.

Ectopic expression

The occurrence of gene expression in a tissue in which it is normally not expressed. Such ectopic expression can be caused by the juxtaposition of novel enhancer elements to a gene during genetic manipulation of transgenic organisms.

Ectopic integrationn

In a transgenic organism, the insertion of an introduced gene (transgene) at a site other than its usual locus.


Organism living on the surface of another organism.

ED 50

The dose of a drug that is pharmacologically effective for 50% of the population exposed to the drug or a 50% response in a biological system that is exposed to the drug. Dose of drug which produces 50% of its maximum response or effect. Alternatively, the dose which produces a pre-determined quantal (all-or-nothing) response in 50% of test subjects or preparations.


Collection of fluid in the tissue causing swelling.

Effect size

Effect size (ES) is a name given to a family of statistical indices that measure the magnitude of a treatment effect.Whereas statistical tests of significance give the likelihood that experimental resultsdiffer from chance expectations, effect-size measurements tell us the relative magnitudeof the experimental treatment. They tell us the size of the experimental effect. Effect sizes are especially important because they allow us to compare the magnitude of experimental treatments from one experiment to another. Although percent improvements can be used to compare experimental treatments to control treatments, such calculations are often difficult to interpret and are almost always impossible to use in fair comparisons across experimental paradigms.
Unlike significance tests, these indices are independent of sample size. ES measures are the common currency of meta-analysis studies that summarize the findings from a specific area of research.
In general, ES can be measured in two ways:
a) as the standardized difference between two means, or
b) as the correlation between the independent variable classification and the individual scores on the dependent variable. This correlation is called the "effect size correlation"


A muscle cell or gland cell that performs the body's responses to stimuli. Responds to signals from the brain or other processing center of the nervous system.


Carrying away from a center or a particular structure. A term applied to nerves and blood vessels.


A term introduced by Stephenson (1956) to describe the way in which agonists vary in the response they produce even when they occupy the same number of receptors. High-efficacy agonists can produce their maximal response while occupying a relatively low proportion of receptors; agonists of lower efficacy cannot activate the receptors to the same degree and may not be able to produce the same maximal response even when they occupy the entire receptor population, thereby behaving as partial agonists. (See relative efficacy).


water that flows from a sewage treatment plant after it has been treated.


The movement of a gas through a small opening from a region of high concentration to a region of low concentration.


A particular extract of Gingko biloba used in Europe to alleviate symptoms associated with several cognitive disorders.


1. A large gamete without flagellae that is fertilized by a sperm cell. An egg cell is also called an ovum.
2. A complex multicellular structure in which an animal embryo develops.
A female gamete, which usually contains abundant cytoplasm and yolk; nonmotile and often larger than a male gamete.


A class of hormones derived from arachidonic acid produced by all cells except Red Blood Cells, that act as local hormones (paracrines) affecting neighboring cells. Eicosanoids include prostaglandins, thromboxanes, and leukotrienes. The eicosanoids can collectively mediate almost every aspect of the inflammatory response. Two groups of eicosanoids, the prostaglandins (PGs) and the leukotrienes (LTs), have a wide range of varying effects that depend upon the nature of the target cell. Eicosanoid activity, for example, may impact blood pressure, blood clotting, immune and inflammatory responses, reproductive processes, and the contraction of smooth muscles.

Ejacultory duct

In the male, a duct from each testis that join to form the urethra.


A type of explosive extrusome found in cryptoflagellates.


An enzyme secreted by neutrophils (white blood cells that engulf pathogens) which catalyzes the cleavage of specific proteins that function to provide elasticity to certain tissues. May be indirectly responsible for some autoimmune diseases, such as arthritis (which results from breakdown of cartilage tissue). Elastase may also be indirectly responsible for the emphysema (caused by loss of lung elasticity) that results from prolonged smoke inhalation. When a-1 antitrypsin (anti-elastase) efficacy is reduced (via smoke) the now-unrestrained excess elastase destroys alveolar walls in the lungs by digesting elastic fibers and other connective tissue proteins.


The ability of a body to regain its original shape after deformation.

Electric current

A flow of electrons through a conductor.  The size of the current is proportional to the rate of electron flow.

Electric potential

The difference in the amount of electric charge between a region of positive charge and a region of negative charge. The establishment of electric potentials across the plasma membrane and across organelle membranes makes possible a number of phenomena, including the chemiosmotic synthesis of ATP, the conduction of nerve impulses, and muscle contraction.

Electrical breakdown

Abrupt rise in electric current in the presence of a small increase in voltage.

Electrical Impedance Scanning

The electrical impedance scanning device, which does not emit any radiation, consists of a hand-held scanning probe and a computer screen that displays two-dimensional images of the breast. An electrode patch, similar to that used for an electrocardiogram, is placed on the patient’s arm. A very small amount of electric current, about the same amount used by a small penlight battery, is transmitted through the patch and into the body. The current travels through the breast, where it is measured by the scanning probe placed over the breast. An image is generated from the measurements of electrical impedance. Different types of tissue have different electrical impedance levels (electrical impedance is a measurement of how fast electricity travels through a given material). Some types of tissue have high electrical impedance, while others have low electrical impedance. Breast tissue that is cancerous has a much lower electrical impedance (conducts electricity much better) than normal breast tissue. Breast tumors may appear as bright white spots on the computer screen.Electrical impedance scanning devices are used along with conventional mammography to detect breast cancer.This device can confirm the location of abnormal areas that were detected by a conventional mammogram. The scanner sends the image directly to a computer, allowing the radiologist to move the probe around the breast to get the best view of the area being examined. The device may reduce the number of biopsies needed to determine whether a mass is cancerous. It may also improve the identification of women who should have a biopsy. The scanner is not approved as a screening device for breast cancer, and is not used when mammography or other findings clearly indicate the need for a biopsy. This device has not been studied with patients who have implanted electronic devices, such as pacemakers. It is not recommended for use on such patients.  (Source: NIH National Cancer Insitute)

Electric field intensity, E

Force on a stationary positive charge per unit charge in an electrical field.

Electrocardiogram or ECG

A recording, from electrodes placed on the surface of the body, of the electrical currents generated by the heart during the cardiac cycle.
The ECG (or EKG) represents a sum of all the concurrent action potentials produced by the heart as detected by the 12 (body surface) electrodes of the electrocardiograph. A single cardiac cycle produces a distinctive wave pattern, where peaks and valleys are indicated by the letters P, Q, R, S, and T. These are interpreted as:
The P wave is a small wave that represents the depolarization of the atria. During this wave, the muscles of the atria are contracting.
The QRS complex is a rapid down-up-down movement. The upward movement produces a tall peak, indicated by R. The QRS complex represents the depolarization of the ventricles.
The T wave represents the repolarization of the ventricles. Electrical activity generated by the repolarization of the atria is concealed by the QRS complex.

Electrochemical gradient

The diffusion gradient of an ion (a chared particle), representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential.

Electroencephalogram or EEG

Electrical activity of the brain recorded from an array of electrodes placed over the scalp.The EEG represents the combined activity of many pyramidal neurones of the cerebral cortex. These cells are oriented perpendicular to the cortical layers. In order to produce detectable waves in the EEG, many pyramidal neurons have to be activated in exact synchrony.  The larger the waves the more synchronous are the activity of the pyramidal cells.
By synchronising the EEG to certain sensory events, acts or decisions also allows the detection of patterns of electrical activity (electrical waves) which reflect the mass activity of neurones in specific brain areas. These are called evoked potentials, as they are electrical events evoked by a specific stimulus. By using large grids of electrodes, the spatial distribution of the evoked potential can be mapped.

Electrogenic pump

An ion transport protein that transports ions asymmetrically (unequal transport in the two directions) across a membrane so that it generates a voltage across the membrane.

Electrohydraulic treatment

Rapid discharge of high voltage electricity across an electrode gap below the surface of aqueous suspensions.


Splitting a substance into the separate chemicals that make it up, by passing an electric current through it.


A chemical compound which can conduct an electric current because it has free ions (thereby allowing movement of charge)

Electromagnetic spectrum

The entire spectrum of radiation; ranges in wavelength from less than a nanometer to more than a kilometre.

Electromagnetic wave

A self-propagating wave in space with electric and magnetic components that oscillate at right angles to each other and the direction of propagation
They are: radio, micro, infra-red, visible light, ultraviolet, X and gamma rays.

Electromyography (EMG)

An insertion of needle electrodes into muscles to study the electrical activity of muscle and nerve fibers. Helps diagnose damage to nerves or muscles.


A subatomic particle with a single negative charge. One or more electrons orbit the nucleus of the atom.

Electron acceptor  

A molecule forming part of the electron transport system; it accepts or receives electrons in an oxidation-reduction reaction, becoming reduced in the process.
Part of the energy carried by the electrons is transferred to ATP, part to NADPH, and part is lost in the transfer system.
Electron carrier = A molecule that can accept and donate electrons from and to various enzymes.
Electron donor = A substance that donates electrons in an oxidation-reduction reaction.
Electron transfer = Movement of electrons from substrates to oxygen via the carriers of the respiratory (electron transport) chain.

Electron capture

An electron in an atom's inner shell is drawn into the nucleus where it combines with a proton, forming a neutron and a neutrino. The neutrino is ejected from the atom's nucleus.Also called K-capture since the captured electron usually comes from the atom's K-shell.
Electron capture is one process that unstable atoms can use to become more stable. Since an atom loses a proton during electron capture, it changes from one element to another. For example, after undergoing electron capture, an atom of carbon (with 6 protons) becomes an atom of boron (with 5 protons) Although the numbers of protons and neutrons in an atom's nucleus change during electron capture, the total number of particles (protons + neutrons) remains the same.

Electron carrier  

A molecule that conveys electrons; one of several membrane proteins in electron transport chains in cells. Electron carriers shuttle electrons during the redox reactions that release energy used to make ATP.

Electron donor  

Substance that donates or gives up electrons in an oxidation-reduction reaction, becoming oxidized in the process.


The tendency for an atom to pull electrons toward itself.

Electronic fetal monitor

The use of external and internal devices that record the fetal heart rate. An externally applied ultrasound transducer converts sound energy into electrical energy which is recorded on a graph. After rupture of the membranes, an electrode can be applied via the maternal vagina to the fetal scalp to obtain a fetal ECG. The maternal uterine contractions also are recorded on the graph so that they can be related to the fetal heart rate, to indicate fetal distress.

Electron microscope

An electron-optical instrument that utilizes a beam of electrons, rather than light, to focus on cell surfaces of a very thin specimen to produce an enlarged image on a fluorescent screen or photographic plate.Because resolution (the ability to distinguish adjacent objects as separate) is better and magnification 1,000 times that of an optical light microscope is possible, electron microscopy can help determine the nature of tumors and of kidney disease. A transmission electron microscope (TEM) is used to study the internal structure of thin sections of cells. A scanning electron microscope (SEM) is used to study the fine details of cell surfaces.

Electron pair geometry

The geometry of where electrons are in relation to a central atom. Electron pairs in four locations will repel and end up 109.5o apart, three locations 120o, two locations 180o and one location no separation of electrons.

Electron shell

An energy level at which an electron orbits the nucleus of an atom.

Electron transport chain

A sequence of electron-carrier molecules (membrane proteins) that shuttle electrons during the redox reactions that release energy used to make ATP.
1) A series of coupled oxidation/reduction reactions where electrons are passed from one membrane-bound protein/enzyme to another before being finally attached to a terminal electron acceptor (usually oxygen or NADPH). ATP is formed by this process. 2) Coupled series of oxidation /reduction reactions during which ATP is generated by energy transfer as electrons move from high reducing state to lower reducing state.

Electron volt

An electron volt is the amount of work done on an electron when it moves through a potential difference of one volt.
1 eV = 1.602*10-19 J = 1.602*10-12 erg = 1.182*10-19 ft-lb = 3.827*10-20 cal

Electrophoresis (also called electrophoretic mobility)

A technique for separating, or resolving the components of a mixture of charged molecules (proteins, DNAs, or RNAs) within a gel or other support, under the influence of an applied electric field. The movement of electrically charged molecules in an electric field often resulting in their separation. Agarose and acrylamide gels are the media commonly used for electrophoresis of proteins and nucleic acids.Dissolved molecules in an electric field move at a speed determined by their charge:mass ratio.  For example if two have the same mass and shape, the one with the greater net charge will move faster toward an electrode.  The separation of small molecules, such as amino acids and nucleotides, is one of the many uses of electrophoresis.  A small drop of sample is deposited on a strip of filter paper or other porous substrate, which is soaked with a conducting solution.  When an electric field is applied to the ends of the strip, small molecules dissolved in the conducting solution move along the strip at a rate corresponding to their magnitude of their charge.


The technique of recording and stimulating currents and voltages across cell membranes using microelectrodes. Electrodes can be used to measure membrane potentials and inject currents. The latter charges the membrane and changes the membrane potentials. If the recorded voltage change is fed back to the stimulating electrode, the current can be adjusted such that the measured membrane potential stays constant. This is called the 'voltage-clamp' technique and has largely been responsible to elucidate the mechanism underlying the electrical phenomena of neurons and muscle tissue.


A technique for transfecting cells by the application of a high-voltage electric field pulses which temporarily destabilizes the lipid bilayer and proteins of cell membranes.


Ionization technique used in mass spectrometry.

Electrotonic potentials

Small depolarisations of a nerve process’s membrane, caused by the passive spread of electrical current through the conducting fluids inside and outside neurons and their processes.
These signals are at least one order of magnitude, and sometimes two or more orders of magnitude, weaker than action potentials in neurons.
The electrotonic spread of current is critical in understanding the generation of action potentials and current flow in neurons and other cells, and depends on four factors:
1. ro: the longitudinal electrical resistance of the extracellular medium;
2. ri: the longitudinal electrical resistance of the intracellular medium, i.e. the axoplasm;
3. rm: the transverse electrical resistance of the membrane, i.e. the neurolemma;
4. cm: the electrical capacity of the membrane.
The flow of current electrotonically can be quantified by the equation:

The space constant, l, is determined as:

Thus if x = l, then the first equation becomes
Vx = V0 e -1
i.e., l is the distance from the point at which current is injected into a cell to the point at which the electrotonic depolarisation has fallen to e -1, i.e. 0.37 (or 37%), of its original value (V0).
l is a useful parameter for comparing electrotonus (the spread of electrotonic current) along neuronal processes of different types and size. Both length and diameter of the process are significant in determining l, e.g., as the diameter of a process increases, the magnitude of l also increases.


Any substance that cannot be broken down to any other substance; A substance composed of atoms all with the same atomic number; An atom with a unique number of protons (atomic number). There are 102 different elements and some additional synthetic elements that are not found in nature. Elements have different physical and chemical properties and can be combined to molecules (two or more atoms linked through covalent bonds). The elements are listed according to atomic number and chemical properties in the periodic table.


The set of all points in a plane such that the sum of the distances to two fixed points is a constant.   
The equation of an ellipse with center at the origin is
x2   +  y2     =     1
a2         b2


A solid of revolution formed by rotating an ellipse about one of its axes.

Elongation factors

Proteins necessary for the proper elongation and translocation processes during translation at the ribosome in prokaryotes.

Embolus / Thrombus

Mass of undissolved matter (foreign object, air, gas, tissue, thrombus) or bubbles (embolus) circulating in the blood or lymphatic channels until it becomes lodged in a vessel


Term applied to the zygote after the beginning of mitosis that produces a multicellular structure; A developing stage of multicellular organisms; in humans, the stage in the development of offspring from the first division of the zygote until body structures begin to appear; about the ninth week of gestation.In humans, there is consensus that the embryo is the developing organism until the end of the eighth week of gestation, when it is called a foetus.  However, there is debate as to the starting point with two broad schools of thought:
Broad definition: That a conceptus is an embryo from the moment of its creation (eg fertilisation). Restricted definition: That a conceptus should be referred to as an embryo only after gastrulation, at which time the cells that will give rise to the future human being can be distinguished from those that form extraembryonic tissues.

Embryoid bodies

Rounded collections of cells that arise when embryonic stem cells are cultured in suspension. Embryoid bodies contain cell types derived from all 3 germ layers.

Embryonic cell layers

See Germ layers

Embryonic germ cells

Pluripotent stem cells that are derived from early germ cells (those that would become sperm and eggs).  Embryonic germ cells (EG cells) are thought to have properties similar to embryonic stem cells.

Embryonic induction

The influence exercised by parts of the embryo, which causes groups of cells to proceed along a particular path of development. Though induction requires that the interacting parts come into close proximity, actual contact is not necessary. The inducing influence—whatever it might be—is a diffusible substance emitted by the activating cells (the inductor). The inducing substance of the mesoderm is a large molecule, probably a protein or a nucleoprotein, which presumably penetrates reacting cells, though direct and unequivocal proof of such penetration is still unavailable. Inducing substances are active on vertebrates belonging to many different classes; e.g., inductions of primary organs have been obtained by transplanting mammalian tissues into frog embryos or by transplanting tissues of a chick embryo into the embryo of a rabbit.
Induction is responsible not only for the subdivision of ectoderm into neural plate and epidermis but also for the development of a large number of organ rudiments in vertebrates. The notochord is a source of induction for the development of the adjoining somites and nephrotomes; the latter appear jointly to induce development of limb rudiments from the lateral plate mesoderm. Further examples are mentioned below in connection with development of the various organs.

Embryonic (or tissue) polarity

The production of axes of asymmetry in a developing embryo or tissue primordium.

Embryonic stem cells

An embryonic cell that can replicate indefinitely, transform into other types of cells, and serve as a continuous source of new cells; The pluripotent stem cells in animals at the very early embryonic development. Primitive (undifferentiated) cells derived from a 5-day pre-implantation embryo that are capable of dividing without differentiating for a prolonged period in culture, and are known to develop into cells and tissues of the three primary germ layers. They have the potential to grow into a complete adult organism

Embryonic stem cell line

Embryonic stem cells which have been cultured under in vitro conditions that allow proliferation without differentiation for months to years

Emission spectrum

The emission spectrum of a substance such as a fluorophore is the intensity of the electromagnetic radiation from the substance as a function of the excitation wavelength of the absorbed light.

Emotional Lability

Exhibiting rapid and drastic changes in emotional state (laughing, crying, anger) inappropriately without apparent reason.


Chronic lung disease in which there is permanent destruction of alveoli from damage to the walls of the alveoli. In emphysema the walls of some alveoli have been damaged and the alveoli lose their elasticity and trap air. Since it is difficult to push all of the air out of the lungs, the lungs do not empty efficiently and therefore contain more air than normal. This air trapping causes lung hyperinflation. The combination of constantly having extra air in the lungs and the extra effort needed to breathe results in a person feeling short of breath. Airway obstruction occurs in emphysema because the alveoli that normally support the airways open cannot do so during inhalation or exhalation. (see Chronic Obstructive Pulmonary Disease)

Empirical Based Curve Fitting

An empirical based standard curve is a method of data reduction which treats all data points as discrete elements and constrains the curve to pass through the mean of each standard response. Empirical methods make the assumption that each standard response mean is the true response of that standard. Each standard point has few degrees of freedom and a low level of statistical reliablility. Empirical methods cannot compensate for the decreased reproducibility at different regions of the standard curve. Empirical methods do not compensate at all for outlier error. Empirically derived standard curves can not be compared statistically to the reference assay standard curves.

Empty set

A set that contains no elements.


Substances which allow the mixing of two or more immiscible liquids (two liquids that don't mix together such as oil and water) to form a stable emulsion. Emulsifiers work by coating the surface of droplets of one liquid in such a way that they can stay dispersed in the second liquid.


Liquid droplets dispersed in another immiscible liquid; tiny droplets of one liquid floating in another liquid, such as oil droplets floating in water. The dispersed phase droplet size ranges from 0.1-10 µm. Important oil-in-water food emulsions, ones in which oil or fat is the dispersed phase and water is the continuous phase, include milk, cream, ice cream, salad dressings, cake batters, flavour emulsions, meat emulsions, and cream liquers. Examples of food water-in-oil emulsions are butter or margarine. Emulsions are inherently unstable because free energy is associated with the interface between the two phases. As the interfacial area increases, either through a decrease in particle size or the addition of more dispersed phase material, i.e. higher fat, more energy is needed to keep the emulsion from coalescing. Some molecules act as surface active agents (called surfactants or emulsifiers) and can reduce this energy needed to keep these phases apart.


One of a pair of molecules that are mirror-image isomers of each other.


Process by which a virus' nucleic acid is enclosed in a capsid.

Encephalization factor

A measure of brain size relative to body size.


Inability to control one's bowels.


A group of organisms that is restricted to a particular geographic area.

Endergonic reaction

A nonspontaneous chemical reaction in which free energy is absorbed from the surroundings; Chemical reactions that require energy input to begin.
A chemical reaction that consumes energy (that is, for which DG is positive).

Ender nail

Also referred to as an Ender rod. A smooth, flexible rod used for intramedullary fixation of long bone fractures. The nail is used for diaphyseal fractures in patients whose epiphyseal growth plates are still open. It is inserted through the metadiaphyseal region, avoiding the epiphyseal plate so that the growth of the bone is not impaired.


within or inside of


Inflammation of the endocardium, the membrane lining the heart.

Endochondral ossification  

The process by which human bones form from cartilage.

Endocrine disruptors

Natural and man-made chemicals that can either mimic or disrupt the action of hormones. Their impact on human biology is still unclear, but they have been implicated in a number of reproductive and health problems in animals.

Endocrine gland

A ductless gland that secretes hormones directly into the bloodstream.

Endocrine system

The complex of structures in the body that produces the chemical agents (hormones) instrumental in maintaining homeostasis and regulating reproduction and development. The internal system of chemical communication involving hormones, the ductless glands that secrete hormones, and the molecular receptors on or in target cells that respond to hormones; functions in concert with the nervous system to effect internal regulation and maintain homeostasis. Unlike exocrine glands, endocrine glands do not secrete substances into ducts but directly into the surrounding extracellular space. The hormones then diffuse into nearby capillaries and are transported throughout the body in the blood. Hormones circulating in the blood diffuse into the interstitial fluids surrounding the cell. Cells with specific receptors for a hormone respond with an action that is appropriate for the cell. Because of the specificity of hormone and target cell, the effects produced by a single hormone may vary among different kinds of target cells.
(see Hormones, HypothalamusPituitary gland)